Aircraft: COMMERCIAL FIXED WING
Phase of flight: Taxi
Anomaly: Deviation / Discrepancy - Procedural Published Material / Policy; Flight Deck / Cabin / Aircraft Event Passenger Misconduct

During single-engine taxi out; the A FA called the cockpit; informing us of passengers' non-compliance with the facemask policy. The decision was made to return to the gate. As we taxied back toward the Ramp; I coordinated with the Captain; advising that I felt it was appropriate to perform an After Landing flow prior to returning to the gate. Captain agreed; and I accomplished the flow. While holding for a gate; and on the apron with the parking brake set; the A FA called back to the cockpit; advising that the passengers were now willing to comply and that the three FAs were comfortable with continuing the flight.At this point we re-accomplished a Before Taxi flow (as appropriate for our single engine taxi configuration); then ran a Before Taxi Checklist. We then coordinated with ATC to proceed with a taxi clearance for departure. The Number 1 engine was started and the rest of the taxi and takeoff proceeded uneventfully. Once airborne; I noticed that we had departed with the autobrake selector in the OFF position. As I thought about the sequence of events leading to that I thought of two things: placing that switch to RTO takes place in the Captain's Before Start flow. I also recalled that when I performed the After Start flow (following the Passenger incident); I placed the Window Heat switches to ON; another item that is normally accomplished in the Captain's Before Start flow.Clearly; in our unique situation; a Before Taxi flow; followed by a Before Taxi Checklist was insufficient to reposition all switches to their appropriate positions prior to taxi and takeoff. Of note; neither of us felt rushed; and we both felt that we used good CRM to methodically think through our situation before continuing; yet in the end; something was missing. I've referenced the manuals; looking for a procedure that would have trapped our errors; but am still left wondering. Since we started the original taxi single engine and never shutdown that engine; the procedure in Flight Ops Manual never entered our minds; yet that guidance probably would've caught the error.Non-standard Ops lead to inadvertent takeoff with auto brakes selected off. On taxi out; the A FA called to tell me that there was a family being non-compliant regarding the face mask policy. I made the decision to taxi back to the gate. I asked the FO to complete the After Landing Checklist. While we were waiting for a gate; the FA called to tell us; 'Never mind; the issue is resolved.' At that point; we completed the Before Taxi Checklist and taxied to the runway. After takeoff; the FO pointed out that RTO switch was not re-selected to 'armed.' Our unique situation made it impossible for autobrake re-selection to occur.In this situation; our normal checklist does not catch the error. I should have triple checked everything because our routine taxi out was interrupted.RTO reengage missed during a taxi back to the gate and subsequent cancellation of that. Air carrier flight crew reported missing re-setting the auto-brake system before takeoff and cited dealing with a passenger not complying with face mask policy as a contributing factor.